Isoflurane in Contrast to Propofol Promotes Fluid Extravasation during Cardiopulmonary Bypass in Pigs

Myocardial perfusion and cardiac dimensions during extracorporeal membrane oxygenation-supported circulation in a porcine model of critical post-cardiotomy failure

Introduction:

Venoarterial extracorporeal membrane oxygenation is widely used as mechanical circulatory support for severe heart failure. A major concern with this treatment modality is left ventricular distension due to inability to overcome the afterload created by the extracorporeal membrane oxygenation circuit. The present porcine study evaluates coronary circulation, myocardial perfusion and ventricular distension during venoarterial extracorporeal membrane oxygenation.

Methods:

Ten anesthetized open-chest pigs were cannulated and put on cardiopulmonary bypass. Heart failure was achieved by 90 minutes of aortic cross-clamping with insufficient cardioplegic protection. After declamping, the animals were supported by venoarterial extracorporeal membrane oxygenation for 3 hours. Continuous haemodynamic measurements were performed at baseline, during cardiopulmonary bypass/aortic cross-clamping and during venoarterial extracorporeal membrane oxygenation. Fluorescent microsphere injections at baseline and after 1, 2 and 3 hours on venoarterial extracorporeal membrane oxygenation evaluated myocardial perfusion. Left ventricular function and distension were assessed by epicardial echocardiography.

Results:

The myocardial injury caused by 90 minutes of ischaemia resulted in a poorly contracting myocardium, necessitating venoarterial extracorporeal membrane oxygenation in all animals. The circulatory support maintained the mean arterial blood pressure within a satisfactory range. A hyperaemic left anterior descending coronary artery flow while on extracorporeal membrane oxygenation was observed compared to baseline. Myocardial tissue perfusion measured by microspheres was low, especially in the subendocardium. Echocardiography revealed myocardial tissue oedema, a virtually empty left ventricle, and a left ventricular output that remained negligible throughout the extracorporeal membrane oxygenation run.

Conclusion:

Coronary artery blood flow is maintained during venoarterial extracorporeal membrane oxygenation after cardiopulmonary bypass and cardioplegic arrest despite severely affected performance of the left ventricle. Myocardial perfusion decreases, however, presumably due to rapid development of myocardial tissue oedema.

Polymer-coated cardiopulmonary bypass circuit attenuates upregulation of both proteases/protease inhibitors and platelet degranulation in pigs

Introduction:

Interaction of blood with a cardiopulmonary bypass (CPB) circuit activates the coagulation-fibrinolysis, complement and kinin-kallikrein systems that are mainly supported by proteases and their inhibitors.

Methods:

Biocompatibility of a new polymer-coated (SEC-coated) CPB circuit was globally evaluated and compared with that of a non-coated CPB circuit by quantitative proteomics, using isobaric tags for relative and absolute quantification labeling tandem mass spectrometry. Plasma samples were taken three times (5 min after initiation of CPB, just before declamping and just before termination of CPB) in 12 pigs undergoing 120 min of CPB with the SEC-coated CPB circuit or a non-coated CPB circuit (n = 6, respectively).

Results:

Identified were 224 proteins having high protein confidence (>99%) and false discovery rate (FDR) <5%. Among these proteins, there were 25 significantly upregulated proteins in the non-coated CPB group compared to those in the SEC-coated CPB group. Dominant protein functions were platelet degranulation, serine-type (cysteine-type) endopeptidase inhibitor activity and serine-type endopeptidase activity in the 25 proteins. Bioinformatics analysis similarly revealed upregulation of proteins belonging to platelet degranulation and negative regulation of endopeptidase activity in the non-coated CPB group; these upregulations were effectively attenuated in the SEC-coated CPB group.

Conclusion:

The new polymer (SEC)-coated CPB circuit effectively attenuated upregulation of proteins compared to the non-coated CPB circuit. These proteins were associated with both proteases/protease inhibitors and platelet degranulation.

Fluid filtration and vascular compliance during cardiopulmonary bypass: effects of two volatile anesthetics

BACKGROUND

As intraoperative fluid accumulation may negatively impact post-operative organ function, strategies minimizing edema generation should be sought for. During general anesthesia, isoflurane in contrast to sevoflurane has been associated with increased fluid extravasation and edema generation. In this study, we tested sevoflurane against isoflurane with focus on vascular compliance and fluid shifts in an experimental cardiopulmonary bypass (CPB) model.

METHODS

Sixteen pigs underwent 120 min of cardiopulmonary bypass with isoflurane or sevoflurane anesthesia. Net fluid balance, plasma volume, serum-electrolytes, serum-albumin, serum-protein, colloid osmotic pressures in plasma and interstitial fluid, hematocrit levels, and total tissue water content were recorded. Intra-abdominal and intracranial pressures were measured directly, and fluid extravasation rates were calculated.

RESULTS

Fluid extravasation rate increased dramatically in both groups during initiation of cardiopulmonary bypass, with no group differences. The animals of the sevoflurane group needed significantly more fluid supplementation to maintain a constant reservoir volume in the CPB circuit during bypass. Plasma volumes prior to bypass were 56.5 ± 7.9 ml/kg (mean ± SD) and 58.7 ± 3.8 ml/kg in the isoflurane group and sevoflurane group, respectively. During bypass, plasma volumes in the isoflurane group decreased about 25%, and remained significantly lowered when compared to the sevoflurane group, where the values remained stable.

CONCLUSIONS

No differences in fluid extravasation rates were observed between sevoflurane and isoflurane. The increased net fluid balance in the sevoflurane group during cardiopulmonary bypass was not associated with edema generation. Plasma volume was retained in the sevoflurane group, in contrast to the isoflurane group.

Continuous positive airway pressure (CPAP) decreases pulmonary shunt in anaesthetized horses

OBJECTIVE

To evaluate the effects of continuous positive airway pressure (CPAP) on intrapulmonary shunt, cardiac output and oxygen delivery in horses subjected to a 6 hour period of general anaesthesia.

STUDY DESIGN

Randomized, experimental, crossover study.

ANIMALS

Ten healthy adult horses.

METHODS

Following medetomidine, diazepam and ketamine administration, orotracheal intubation was performed and horses positioned in dorsal recumbency. Anaesthesia was maintained with isoflurane carried in an oxygen and air mix (FiO₂ 0.5) combined with a medetomidine infusion. Horses were anaesthetized twice and either CPAP (8 cmH₂ O) or physiologic airway pressure (NO CPAP) was applied to the lungs for 6 hours; the order of treatments was randomly assigned. Following induction of anaesthesia, cardiovascular and respiratory variables (including arterial blood gas analysis) were recorded every 30 minutes, cardiac output was measured every 60 minutes using the lithium dilution technique and oxygen delivery calculated. If PaCO₂ exceeded 100 mmHg (13.3 kPa), controlled ventilation was initiated and horses excluded from further data collection. Groups were compared using a general linear model.

RESULTS

Data from eight horses were analysed. PaO₂ was 15-56 mmHg (2.00-7.45 kPa) higher (p < 0.001) and shunt fraction 6-14% lower (p < 0.001) in the CPAP group. No differences were seen for cardiac output and oxygen delivery. The lack of difference in oxygen delivery was attributed to lower haemoglobin levels in the CPAP group than in the NO CPAP group.

CONCLUSIONS AND CLINICAL RELEVANCE

CPAP of 8 cmH₂ O can be used in dorsally recumbent horses to decrease pulmonary shunt fraction without causing a decrease in cardiac output during longterm anaesthesia.

Interstitial fluid colloid osmotic pressure in healthy children

Objective

The colloid osmotic pressure (COP) of plasma and interstitial fluid play important roles in transvascular fluid exchange. COP values for monitoring fluid balance in healthy and sick children have not been established. This study set out to determine reference values of COP in healthy children.

Materials and Methods

COP in plasma and interstitial fluid harvested from nylon wicks was measured in 99 healthy children from 2 to 10 years of age. Nylon wicks were implanted subcutaneously in arm and leg while patients were sedated and intubated during a minor surgical procedure. COP was analyzed in a colloid osmometer designed for small fluid samples.

Results

The mean plasma COP in all children was 25.6 ± 3.3 mmHg. Arbitrary division of children in four different age groups, showed no significant difference in plasma or interstitial fluid COP values for patients less than 8 years, whereas patients of 8-10 years had significant higher COP both in plasma and interstitial fluid. There were no gender difference or correlation between COP in interstitial fluid sampled from arm and leg and no significant effect on interstitial COP of gravity. Prolonged implantation time did not affect interstitial COP.

Conclusion

Plasma and interstitial COP in healthy children are comparable to adults and COP seems to increase with age in children. Knowledge of the interaction between colloid osmotic forces can be helpful in diseases associated with fluid imbalance and may be crucial in deciding different fluid treatment options.

Trial Registration

ClinicalTrials.gov NCT01044641

Does insulin impact cold-induced fluid- and protein-extravasation?

BACKGROUND

Insulin has been shown to stabilize the endothelial barrier via inactivation of the endothelial contractile machinery and enhancement of cell-cell adhesions. Here we explored if insulin by its endothelial-stabilizing and anti-inflammatory properties could influence the increase of fluid- and protein-extravasation during hypothermia.

METHODS

Two groups of animals (n=10, each) were cooled to 28°C, with insulin-infusion (I-group) or without (C-group), in a randomly controlled study. Fluid balance, hemodynamics, plasma volume (PV), colloid osmotic pressures in plasma (COPp) and interstitial fluid (COPi), hematocrit (Hct), cytokine profiles, serum-albumin- and protein-concentrations were measured and fluid extravasation rate (FER) and albumin-and protein-masses calculated.

RESULTS

During 240 min of hypothermia the albumin- and protein-masses together with COPp decreased significantly in both groups. COPi remained essentially unchanged. Plasma volume decreased significantly in the C-group, whereas only a decreasing trend was present in the I-group. Hemoconcentration was significant in both study groups reflected by the Hct-values. A slight increasing trend of FER was seen in both groups from 0.10 (0.04) ml/kg/min and 0.09 (0.05) mg/kg/min, C-group and I-group, respectively, to 0.14 (0.05) mg/kg/min and 0.12 (0.03) mg/kg/min, during the hypothermic period. Between-group differences were absent for all listed parameters including FER.

CONCLUSION

Insulin administration does not impact fluid and protein extravasation significantly in animals undergoing cooling and prolonged hypothermia.